Cisco Cisco Email Security Appliance C160 Guía Del Usuario
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Cisco AsyncOS 9.0 for Email User Guide
Chapter 13 Anti-Spam
Determining Sender IP Address In Deployments with Incoming Relays
•
Custom Header
Using custom headers is the recommended method of identifying original senders. The machine
connecting to the original sender needs to add this custom header. The value of the header is expected
to be the IP address of the external sending machine. For example:
connecting to the original sender needs to add this custom header. The value of the header is expected
to be the IP address of the external sending machine. For example:
SenderIP: 7.8.9.1
X-CustomHeader: 7.8.9.1
If your local MX/MTA can receive mail from a variable number of hops, inserting a custom header is
the only way to enable the Incoming Relays feature. For example, in
the only way to enable the Incoming Relays feature. For example, in
to IP address 10.2.3.5; however, path C has two hops and path D has one. Because the number of hops
can vary in this situation, you must use a custom header in order to have Incoming Relays configured
correctly.
can vary in this situation, you must use a custom header in order to have Incoming Relays configured
correctly.
Figure 13-6
Mail Relayed by MX/MTA — Variable Number of Hops
Related Topics
•
Received Header
If configuring the MX/MTAs to include a custom header containing the sending IP address is not an
option, you can configure the incoming relays feature to attempt to determine the sending IP address by
examining the “Received:” headers in the message. Using the “Received:” header will only work if the
number of network “hops” will always be constant for an IP address. In other words, the machine at the
first hop (10.2.3.5 in
option, you can configure the incoming relays feature to attempt to determine the sending IP address by
examining the “Received:” headers in the message. Using the “Received:” header will only work if the
number of network “hops” will always be constant for an IP address. In other words, the machine at the
first hop (10.2.3.5 in
) should always be the same number of hops away from the edge of your
Cisco IronPort Email Security appliance
Firewall
MX
Sending
Machine
Machine
IP: 7.8.9.1
IP: 10.2.3.4
IP: 10.2.3.6
MTA
IP: 10.2.3.5
Hop 2
Hop 1
C
D